Generating changelog:
Sorting tags..
Generating log..
/Library/Ruby/Gems/2.0.0/gems/github_changelog_generator-1.2.0/lib/github_changelog_generator.rb:326:in `get_time_of_tag': undefined method `[]' for nil:NilClass (NoMethodError)
        from /Library/Ruby/Gems/2.0.0/gems/github_changelog_generator-1.2.0/lib/github_changelog_generator.rb:207:in `generate_log_between_tags'
        from /Library/Ruby/Gems/2.0.0/gems/github_changelog_generator-1.2.0/lib/github_changelog_generator.rb:246:in `generate_log_before_tag'
        from /Library/Ruby/Gems/2.0.0/gems/github_changelog_generator-1.2.0/lib/github_changelog_generator.rb:159:in `generate_log_for_all_tags'
        from /Library/Ruby/Gems/2.0.0/gems/github_changelog_generator-1.2.0/lib/github_changelog_generator.rb:128:in `compund_changelog'
        from /Library/Ruby/Gems/2.0.0/gems/github_changelog_generator-1.2.0/bin/github_changelog_generator:4:in `<top (required)>'
        from /usr/bin/github_changelog_generator:23:in `load'
        from /usr/bin/github_changelog_generator:23:in `<main>'